DC motors are known from the prior art. These have, for example, an armature or rotor provided with coils that are supplied with electric energy via a commutator with a brush arrangement. When a fault occurs, it is possible owing to jamming of the rotor, for example because of loose components in the interior of the DC motor, on the one hand, or, on the other hand, owing to a fault in the downstream system driven by the DC motor for the rotor to be blocked and thereby, possibly, for this to lead to damage or destruction of the drive electronics and of the DC motor by overheating if the DC motor continues to be powered. Consequently, an attempt is usually made to detect blocking of the DC motor at an early stage in order to interrupt the current flow through the DC motor when blocking is detected.
The blocking of a DC motor is usually carried out on the basis of speed monitoring in which a speed sensor is used to detect a profile of the speed. If, despite powering of the DC motor, no movement of the rotor is detected, it is possible to infer blocking of the motor. However, this method assumes that a speed sensor has been provided. This is expensive, and it is desirable to save the additional component of a speed sensor.
In modern motor systems, an attempt is therefore made to carry out speed detection without sensors, solely on the basis of an evaluation of a current profile through the DC motor. It is possible for this purpose to monitor a motor current, it being assumed that the blocked DC motor has a substantially higher current consumption than would be the case for a DC motor under load functioning correctly.
However, given increased wear of the DC motor, for example given pasting, given jamming of brushes on the commutator lamellae, given wear of the brush electrodes, and the like, it is possible for states to occur in which even a blocked DC motor does not occasion such a substantially increased motor current that said motor can be detected as blocked with the aid of the above method of current monitoring.
It is therefore desirable to make available a method and a device for detecting blocking or sluggishness of a DC motor in the case of which blocking can be reliably detected even when there is no substantially increased motor current given a motor that is blocked because of an age-induced degradation of components.